3.3 Opposing Changes in Rainfall Properties: Increased Conditional Rain Rates, Decreased Duration and Areal Coverage
Changes in the event-based areal mean rainfall accumulation are examined through changes in three rainfall components: mean conditional rain rate, event duration, and rain area (Fig. 5, Fig. S4-S5). The mean conditional rain rate significantly increases with an average change of 15%, and >85% of the events show higher average conditional rain rate in the future compared with the historic simulations. Although there is some correlation between the changes in mean conditional rain rate and total rainfall (Spearman’s correlation:\(\rho=0.37\); Fig. S5) increases as large as 47% (event #16) are observed in events with a reduction of the rainfall accumulation. This suggests that the change in the mean conditional rain is rather weakly related to rainfall accumulation.
While mean conditional rain rate is increasing, the duration of events shows a significant negative change (-9%), from a mean of 3290 min to 2980 min, and >75% of the events are longer in historic compared to future simulations (Table 1). The reduction in durations is not, however, a good predictor for the reduction in total rainfall accumulation, with a low, non-significant negative correlation between the two (Fig. S5).
The third component in this analysis, the rain area, reveals the largest relative change out of all three components. It also presents the highest correlation with the change in rainfall accumulation (\(\rho=0.93\); Fig. S5). The rain area is decreased in all but one of the events (>97% of events) with a significant and substantial average decrease (-40%). Events with the lowest reduction (or even slight increase) in rainfall accumulation are only those in which the reduction in the rain area is relatively small, while events with a large decrease in rainfall accumulation are accompanied by a large decrease in rain area. These results indicate that the factor most heavily related to changes in rainfall accumulation is the rain area.